San Diego Management & Monitoring Program


Pallid bat
Antrozous pallidus

Vertebrata
Microchiroptera

Vertebrata Microchiroptera
Kingdom Phylum Subphylum Class Order Suborder Family

Current distribution rangewide

Ranges throughout western North America, from British Columbia's southern interior, south to Queretaro and Jalisco, and east to Texas [1]. Common throughout arid deserts and grasslands in the southwestern U.S. [2]. Distribution in Washington and Oregon includes Sonoran and Transitional life zones. Occurs throughout most of California except for the high Sierra Nevada Mountains and the northwestern corner of the state [3]. Historically abundant in the coastal plains, inland valleys, and western foothills of San Diego County [4 cited from 5].


Known Populations in San Diego County

Occurrences found in Buena Vista Lagoon Ecological Reserve, Kendall Frost Marsh, Tijuana Slough National Wildlife Refuge, Tijuana River Valley Regional Park, San Diego River Park, San Diego Bay National Wildlife Refuge, Torrey Pines State Natural Reserve, Agua Hedionda-SDGE, San Elijo Lagoon Ecological Reserve, Escondido Creek Preserve, Agua Hedionda Lagoon Ecological Reserve, San Luis Rey River Park, Batiquitos Lagoon Ecological Reserve, Flood Control Channel Southern Wildlife Preserve, San Dieguito River Park, Buena Vista Lagoon Ecological Reserve, San Dieguito Lagoon, Otay Lakes Cornerstone Lands, Los Penasquitos Canyon Preserve, and Torrey Pines


List status

SSC


Habitat affinities

Occurs in a wide variety of habitats, including grasslands, shrublands, woodlands, and forests. Most common in open, dry habitats with rocky areas for roosting [3]. A yearlong resident over most of its range, often found roosting in rural man-made structures such as barns or other infrequently used buildings [4 cited from 5]. Locally common species of low elevations in California [3].


Taxonomy and genetics

Member of the taxonomic Order Chiroptera and Family Vespertilionidae and is currently the only member of its genus [6].


Seasonal activity

Nocturnal. Emerges late (30-60 min after sunset), with a major activity peak 90-190 min after sunset, and a second peak shortly before dawn. Brief foraging periods occur in autumn, and activity is infrequent below 2°C. Undergoes shallow torpor daily. Hibernates in winter near the summer day roost [2]. Duration of the daytime roosting period differs sharply from season to season, probably at least partly in response to day length, temperature, and insect abundance [7].


Life history/ reproduction

Maternity colonies form in early April, and may have a dozen to 100 individuals. Males may roost separately or in the nursery colony [3]. Mates from late October-February. Fertilization is delayed, gestation is 53-71 days. Young are born from April-July, mostly from May-June. Litter size is 1-3. Average litter is 2, but females reproducing for the first time usually have 1 young. Altricial young are weaned in 7 weeks and are observed flying in July and August. Females nurse only their own young. Females and juveniles forage together after weaning. Females mate in first autumn, males in second. Maximum recorded longevity is 9 yr,1 mo [8].


Diet and foraging

Takes a wide variety of insects and arachnids, including beetles, orthopterans, homopterans, moths, spiders, scorpions, solpugids, and Jerusalem crickets. It is able to consume large, hard-shelled prey [9]. Foraging is concentrated in two periods at the beginning and end of the nocturnal cycle of activity during most of the active season [2]. Occurs over open ground, usually 0.5-2.5 m above ground level. Flight is slow and maneuverable with frequent dips, swoops, and short glides. Many prey are taken on the ground. Gleaning frequently used and a few prey are taken aerially. Can maneuver well on the ground. May carry large prey to a perch or night roost for consumption. Uses echolocation for obstacle avoidance; possibly utilizes prey-produced sounds while foraging [3]. Usually found foraging in oak savannah-type habitats, grassy oak and sycamore-lined river terraces, native grasslands, and sparsely vegetated scrublands [4 cited from 5].


Dispersal

Forages 0.5-2.5 km (1-3 mi) from day roost. Capable of homing from distances of a few miles, but not further [3].


Threats

Threatened by damage and destruction of roosts and hibernacula through vandalism, mine closures and reclamation, recreational activities such as rock climbing, and forestry practices such as timber harvest. Roosts and hibernicula are also threatened when man-made structures are occupied, demolished, modified, have chemical treatments applied, or when bats are intentionally eradicated and excluded. Other threats include loss or modification of foraging habitat due to prescribed fire, urban development, agricultural expansion, and/or pesticide use [1;10].


Pallid bat sources